Known automatic or automated motor vehicle transmissions normally feature a parking lock with which an output shaft of the transmission can be mechanically immobilized. In addition to a purely mechanical system for actuating such a parking lock by way of a mechanical functional connection between a gear selector lever operated by the driver in the interior of the motor vehicle and the parking lock in the transmission, electromechanical and electrohydraulic systems for actuating such a parking lock are known from DE 4127991 C2. The parking lock in the transmission is connected by way of an electrical functional connection with a selector device that can be operated by the driver in the interior of the motor vehicle, and in which case the parking lock can be electromechanically, or as the case may be electrohydraulically actuated such that a parking lock function implemented by an electronic control device of the transmission, subject to a drive position selected on the selector device and subject to other operating parameters of the motor vehicle.
In addition, different methods are known for automatically engaging such a parking lock. It is thus proposed in U.S. Pat. No. 3,937,105 that the parking lock of the transmission is automatically engaged independently of the drive position selected by the driver when an ignition circuit of the motor vehicle is interrupted and, at the same time, the motor vehicle's velocity is lower than a defined low threshold level.
In U.S. Pat. No. 4,892,014, a method is known in which the parking lock of the transmission is automatically, electromotively engaged when an ignition circuit of the motor vehicle is interrupted and, at the same time, the velocity of the motor vehicle is lower than a defined threshold, but also when the driver's door of the motor vehicle is open and the driver's seat of the motor vehicle is not occupied and, at the same time, the speed of the vehicle is lower than the cited low threshold level. In both cases, it is provided that when the parking lock is automatically engaged, a parking brake of the motor vehicle will also be automatically actuated. In U.S. Pat. No. 4,892,014, it is also proposed that when the ignition circuit is closed, without the drive motor of the motor vehicle running, the transmission will automatically, electromotively switch to its neutral position without the necessity of a command from the driver.
And finally, from EP 0 814 287 B1, a function for automatically engaging the parking lock of an automatic transmission is known in which the parking lock in the automatic transmission is automatically engaged byway of the gear control device when the driving speed of the vehicle is zero and, at the same time, an ignition circuit is interrupted and, at the same time, as a supplementary condition, either a predetermined period of time after the interruption of the ignition circuit has passed or a vehicle door has been opened, however no later—and then as the sole condition—that the ignition key has been removed from the ignition switch.
In order to achieve better vehicle availability, the engagement of the parking lock is prevented as a distinctive feature in all three cases, when the driver immediately, before turning off the engine or within a predetermined period of time after switching off the engine, has selected the drive state neutral using the selector lever.
The present invention is based upon the objective of devising an alternative method to the state of the art for automatically controlling a neutral position and a parking lock in an automatic or automated transmission of a motor vehicle with adequate safeguarding of the motor vehicle against starting or coasting of the vehicle that is not intended by the driver and with as little impairment of drivability or maneuverability of the vehicle as possible, while avoiding changes in the operating state of the transmission or the vehicle, which would be surprising for the driver.